$\textit{Ab initio}$ evidence for nonthermal characteristics in ultrafast laser melting

TL;DR

This study provides ab initio evidence that ultrafast laser melting of silicon occurs through a nonthermal process driven by electronic excitation, not lattice heating, challenging traditional thermal models.

Contribution

The paper demonstrates nonthermal laser melting in silicon using real-time density functional theory, revealing electronic excitation as the primary driver, unlike previous thermal assumptions.

Findings

Nonthermal melting occurs at temperatures below 1680 K.

Excitation-induced changes in bonding electron density drive melting.

Experimental diffraction intensity evolution aligns with simulation results.

Abstract

Laser melting of semiconductors has been observed for almost 40 years; surprisingly, it is not well understood where most theoretical simulations show a laser-induced thermal process. $\textit{Ab initio}$ nonadiabatic simulations based on real-time time-dependent density functional theory reveal intrinsic nonthermal melting of silicon, at a temperature far below the thermal melting temperature of 1680 K. Both excitation threshold and time evolution of diffraction intensity agree well with experiment. Nonthermal melting is attributed to excitation-induced drastic changes in bonding electron density, and the subsequent decrease in the melting barrier, rather than lattice heating as previously assumed in the two-temperature models.